Packaging laminate for a retortable packaging container

ABSTRACT

A packaging laminate for a retortable packaging container, the packaging laminate ( 30 ) including a paper or paperboard layer ( 31 ), outer, liquid-tight coatings ( 32; 33 ) and an aluminium foil ( 34 ) serving as gas barrier between the paper or paperboard layer ( 31 ) and one of the two outer liquid-tight coatings ( 32 ). In order to compensate for or counteract possible loss of gas tightness because of crack formations or similar untightness in the tensile-sensitive aluminium foil ( 34 ), the packaging laminate ( 30 ) includes at least one additional layer ( 35 ) serving as gas barrier between the paper or paperboard layer ( 31 ) and the aluminium foil ( 34 ). Preferably, said at least one additional gas barrier layer ( 35 ) is bonded to the paper or paperboard layer ( 31 ) by an interjacent lamination or adhesive layer ( 36 ) of polypropylene or other olefin polymer, whereby the thickness or quantity of the additional gas barrier layer ( 36 ) may be reduced without deterioration in gas tightness properties in the finished packaging container.

TECHNICAL FIELD

The present invention relates to a packaging laminate for a retortablepackaging container comprising a core layer, outer, liquid-tightcoatings and an aluminium foil between the core layer and the one outercoating and serving as a gas barrier.

BACKGROUND ART

A packaging laminate of the type which is described above is known from,for example, international patent application carrying publicationnumber WO97/02140. The prior art packaging laminate has a rigid, butfoldable core layer of paper or paperboard and outer, liquid-tightcoatings of moisture and heat resistant plastic material on both sidesof the core layer. In order to impart to the prior art packaginglaminate tightness properties also against gases, in particular oxygengas, the packaging laminate moreover displays an aluminium foil whichserves as gas barrier and which is disposed between the paper orpaperboard layer and the one outer plastic coating.

From the prior art packaging laminate, retortable packaging containersare produced with the aid of filling machines of the type which, from aweb or from prefabricated blanks of the packaging laminate, form filland seal finished packages in accordance with the so-calledform/fill/seal principle well-known in packaging contexts.

From, for example, a flat folded tubular packaging blank of the priorart packaging laminate, retortable packaging containers are produced inthat the packaging blank is first raised to an open, tubular packagingcarton which is sealed at its one end by fold forming and thermosealingof continuous, foldable end panels of the packaging carton, for theformation of a substantially planar bottom closure. The packaging cartonprovided with a bottom is filled with the relevant contents, e.g. food,through its open end which is thereafter sealed by an additional foldforming and thermosealing of corresponding end panels of the packagingcarton for the formation of a substantially planar top closure. Thefilled and sealed, normally parallelepipedic packaging container isthereafter ready for a heat treatment in order to impart to the packedcontents or food extended shelf-life in its unopened packagingcontainer.

A heat treatment which extends shelf-life may suitably be carried intoeffect in the manner and under the conditions described in internationalpatent application carrying publication number WO98/16431 which ishereby incorporated as reference. The packaging container is, in thisinstance, placed in a retort and is heated therein with the aid of afirst gaseous medium flowing in contact with the outer walls of thepackaging container, e.g. hot steam, to a temperature generally withinthe range of 70-130° C. After a predetermined stay time at the selectedtemperature, the supply of the gaseous medium is discontinued. Thepackaging container is cooled with a second, circulating gaseous medium,e.g. cold air, and finally with a circulating liquid medium, e.g. coldwater. The cooled, retorted packaging container is thereafter removedfrom the retort for storage, transport and/or other handling.

Even if a packaging container of the prior art packaging laminatewithstands, in normal cases, a rough heat treatment which retortingentails, it nevertheless not seldom occurs that the aluminium foilembodied as gas barrier is, during the reforming of the packaginglaminate into packaging containers, subjected to such powerful tensilestresses that it cracks in particularly exposed regions of the packaginglaminate. The occurrence of cracks in the tensile-sensitive aluminiumfoil entails that the packaging container correspondingly losestightness properties against gases which can thereby penetrate into thepackaging container and come into contact with the packed product. Theproblem with undesirable penetration of gases through cracks which haveoccurred in the aluminium foil becomes particularly serious in thosecases when the packed product is particularly sensitive to the action ofgases, e.g. oxygen gas, which may very rapidly destroy a product andrender it unusable.

One object of the present invention is, therefore, to obviate theabove-described drawback in connection with the prior art packaginglaminate.

A further object of the present invention is to provide a packaginglaminate of the type described by way of introduction which may readilybe reformed by fold forming and thermosealing into a retortablepackaging container without the risk that the packaging container losesits desirable tightness properties against gases, in particular oxygengas, even if the tensile-sensitive aluminium foil is subjected to crackformation and similar untightness during fold forming of the packaginglaminate.

Yet a further object of the present invention is to provide a retortablepackaging container produced from the packaging laminate for perishableand oxygen gas-sensitive food products.

These and other objects and advantages will be obtained according to thepresent invention by a packaging laminate and by a packaging containerproduced from the packaging laminate as described herein. Expedientembodiments of the packaging laminate according to the present inventionhave further been given characterizing features as described herein.

SUMMARY OF THE INVENTION

Thus, the present invention provides a packaging laminate for aretortable packaging container comprising a core layer, outer,liquid-tight coatings and an aluminium foil which serves as a gasbarrier and which is disposed between the core layer and the one outercoating, the packaging laminate including, for the purpose of promotinggas tightness, a further layer serving as gas barrier between the corelayer and the aluminium foil.

The present invention also provides a retortable packaging container forparticularly perishable and oxygen gas-sensitive products produced byfold forming and sealing of the packaging laminate according to thepresent invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

The present invention will now be described and explained in greaterdetail hereinbelow with particular reference to the accompanyingDrawing. In the accompanying Drawing:

FIG. 1 schematically shows the general structure of a packaging laminatefor a retortable packaging container according to the prior arttechnology;

FIG. 2 schematically shows the general structure of a packaging laminatefor a retortable packaging container according to a first embodiment ofthe present invention; and

FIG. 3 schematically shows the general structure of a packaging laminatefor a retortable packaging container according to a preferred embodimentof the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS AND THE ACCOMPANYING DRAWING

FIG. 1 shows the general structure of a prior art packaging laminatecarrying the generic reference numeral 10. The packaging laminate 10 hasa rigid, but foldable core layer 11 of paper or paperboard, as well asouter, liquid-tight coatings 12 and 13 on both sides of the core layer11. The packaging laminate 10 further displays an aluminium foil 14serving as gas barrier and disposed between the core layer 11 and theone outer, liquid-tight coating 12.

From the prior art packaging laminate 10, a retortable packagingcontainer is produced in a per se known manner by fold forming andthermosealing of a sheet-or web-shaped blank of the packaging laminate10. From, for example, a flat-folded tubular packaging blank, such aretortable packaging container is produced in that the packaginglaminate is first raised to an open, tubular packaging carton whose oneend is sealed by fold forming and thermosealing of continuous, foldableend panels of the packaging carton for the formation of a substantiallyplanar bottom closure. The packaging carton with the closed bottom isfilled with the relevant contents, e.g. a food, through its open end andis thereafter given a substantially planar top closure by additionalfold forming and thermosealing of corresponding continuous, foldable endpanels of the packaging carton. The thus filled and closed, normallyparallelepipedic packaging container is thereafter ready for a heattreatment in a retort in order to impart to the packed contents or foodso-called extended shelf-life in the unopened packaging container.

The problem inherent in the prior art packaging laminate 10 is, as hasalready been described, that the aluminium foil 14 included in thepackaging laminate can, because of its tensile sensitivity, crack, inparticular in areas where tensile stresses on the aluminium foil areparticularly powerful during the reforming of the packaging laminateinto a packaging container, and that the produced packaging containerthereby loses tightness properties against gases. Such cracks andsimilar untightness in the aluminium foil of the packaging laminate can,in certain cases, be so extensive and serious that the packagingcontainer becomes totally unusable, in particular if the packagingcontainer is intended to be used for particularly perishable and oxygengas-sensitive foods which would rapidly be destroyed and deteriorate inquality if they came into contact with oxygen gas.

The problem in connection with the above-described, prior art packaginglaminate 10 is solved in a simple manner and using simple means by apackaging laminate according to the present invention with a structureillustrated schematically in FIG. 2.

The packaging laminate carrying the generic reference numeral 20 in FIG.2 similarly displays a rigid, but foldable core layer 21 of paper orpaperboard and outer, liquid-tight coatings 22 and 23. Between the corelayer 21 and the one outer, liquid-tight coating 22, the packaginglaminate 20 has an aluminium foil 24 serving as gas barrier.

The packaging laminate 20 according to the present invention differsfrom the prior art packaging laminate 10 in FIG. 1 principally in thatit displays, between the aluminium foil 24 and the core layer 21, anadditional layer 25 serving as gas barrier in order to compensate for orcounteract possible cracks which may occur in the aluminium foil 24 whenthe packaging laminate 20 is reformed into a packaging container.

Preferred materials for the additional or supplementary gas barrierlayer 25 in the packaging laminate 20 according to the present inventionmay be selected from the group essentially comprising polyethyleneterephthalate (PET), amorphous polyethylene terephthalate (APET), cyclicolefin copolymers (COC), polyamide (PA), amorphous polyamide (APA),liquid crystalline polymers (LCP), ethylene vinyl alcohol. copolymers(EVOH) and polyvinyl alcohol (PVOH) which may possibly be applied on athin carrier layer, such as, for example, paper.

The outer, liquid-tight coating 23 may be a plastic which is selectedfrom the group essentially comprising polyethylene (PE), polypropylene(PP) and polyester (PET), or mixtures thereof. Examples of a usablepolyethylene plastic may be high density polyethylene (HDPE) or linearlow density polyethylene (LLDPE), an example of a usable polypropyleneplastic may be oriented polypropylene (OPP), and an example of a usablepolyester plastic may be amorphous polyester (APET).

Preferably, the liquid-tight coating 23 consists of a physical ormechanical mixture of polypropylene (PP) and polyethylene (PE) which, inaddition to superior tightness properties against liquid, also hassufficient moisture and heat resistance to withstand such extrememoisture and temperature stresses as occur in a normal heat treatment ina retort for extending shelf-life. An outer coating 23 of a physical ormechanical mixture of polypropylene (PP) and polyethylene (PE) moreoverdisplays superior printability, at the same time as making formechanically strong and liquid-tight seals by thermosealing when thepackaging laminate 20 is reformed into retortable packaging containers.

The thickness or quantity of the outer, liquid-tight coating 23 may varywithin broad limits, but is generally 25-45 g/m².

Correspondingly, the outer, liquid-tight coating 22 may consist of aplastic which is selected from the group essentially comprisingpolyethylene (PE), polypropylene (PP), polyester (PET) and copolymersthereof. An example of a usable polyethylene plastic may be a highdensity polyethylene (HDPE) or a linear low density polyethylene (LLDPE)and an example of a usable polyester plastic may be an amorphouspolyester (APET).

Preferably, the liquid-tight coating 22 consists of a copolymer ofpropylene and ethylene which is sufficiently moisture and heat-resistantto withstand extreme moisture and temperature stresses which occur in anormal heat treatment in a retort intended to extend shelf-life. Acoating of a copolymer of propylene and ethylene moreover makes formechanically strong and liquid-tight seals when the packaging laminate20 is reformed into a packaging container for retorting purposes.

The thickness or quantity of the outer plastic coating 22 may varywithin broad limits, but is generally within the range of 25-35 g/m².

While a packaging container which is produced by fold forming andsealing of the prior art packaging laminate 10 in FIG. 1 not seldomloses desirable tightness properties against gases, in particular oxygengas, because of cracks which may occur in the aluminium foil 14 when thepackaging laminate 10 is reformed into a packaging container, this riskis effectively counteracted or obviated by the layer 25 employed as anadditional gas barrier between the core layer 21 and the aluminium foil24 in the packaging laminate 20 according to the present invention. Thequantity or thickness of the layer 25 in the illustrated embodiment isin general 10-30 g/m².

FIG. 3 schematically illustrates a packaging laminate 30 according toone preferred embodiment of the present invention. The packaginglaminate 30 includes a rigid, but foldable core layer 31 of paper orpaperboard and outer, liquid-tight coatings 32 and 33. Between the corelayer 31 and one of the two outer, liquid-tight coatings 32, thepackaging laminate 30 has an aluminium foil 34 serving as gas barrier.

The packaging laminate 30 according to this preferred embodiment differsfrom the prior art packaging laminate 10 in FIG. 1 in the same manner asthe packaging laminate 20 in FIG. 2 principally in that, between thealuminium foil 34 and the core layer 31, it has an additional layer 35serving as gas barrier to compensate for or counteract possible crackswhich may occur in the aluminium foil 34 when the packaging laminate 30is reformed into a packaging container.

Preferred materials for the additional or supplementary gas barrierlayer 35 in the packaging laminate 30 may be selected from the groupessentially comprising polyethylene terephthalate (PET), amorphouspolyethylene terephthalate (APET), cyclic olefin copolymers (COC),polyamide (PA), amorphous polyamide (APA), liquid crystalline polymers(LCP), ethylene vinyl alcohol copolymers (EVOH) and polyvinyl alcohol(PVOH) which may optionally be applied on a thin carrier layer, such as,for example, paper.

The outer, liquid-tight coating 33 may be a plastic which is selectedfrom the group essentially comprising polyethylene (PE), polypropylene(PP) and polyester (PET), or mixtures thereof. Examples of a usablepolyethylene plastic may be high density polyethylene (HDPE) or linearlow density polyethylene (LLDPE), an example of a usable polypropyleneplastic may be oriented polypropylene (OPP) and an example of a usablepolyester plastic may be amorphous polyester (APET). Preferably, theliquid-tight coating 33 consists of a physical or mechanical mixture ofpolypropylene (PP) and polyethylene (PE) which, in addition to superiortightness properties vis-à-vis liquid, also displays sufficient moistureand heat-resistance to withstand such extreme moisture and temperaturestresses as occur in a normal heat treatment in a retort for extendingshelf-life. An additional coating 33 of a physical or mechanical mixtureof polypropylene (PP) and polyethylene (PE) moreover displays superiorprintability, at the same time as it makes for mechanically strong andliquid-tight seals by thermosealing when the packaging laminate 33 isreformed into retortable packaging containers.

The thickness or quantity of the outer liquid-tight coating 33 may varywithin broad limits, but is in general within the range of 25-45 g/m².

Correspondingly, the outer, liquid-tight coating 32 may consist of aplastic which is selected from the group essentially comprisingpolyethylene (PE), polypropylene (PP), polyester (PET) and copolymersthereof. Examples of a usable polyethylene plastic may be a high densitypolyethylene (HDPE) or a linear low density polyethylene (LLDPE) and anexample of a usable polyester plastic may be an amorphous polyester(APET).

Preferably, the liquid-tight coating 32 consists of a copolymer ofpropylene and ethylene which is sufficiently moisture and heat-resistantto withstand extreme moisture and temperature stresses which occur in anormal heat treatment for extending shelf-life which is carried out in aretort. A coating of a copolymer of propylene and ethylene moreovermakes for mechanically strong and liquid-tight seals when the packaginglaminate 30 is reformed into a packaging container for retortingpurposes.

The thickness or quantity of the outer plastic coating 32 may varywithin broad limits, but is in general within the range of 25-35 g/m².

As is illustrated schematically in FIG. 3, the layer 35 used asadditional gas barrier is bonded to the core layer 31 by at least oneinterjacent lamination or adhesive layer 36. By a suitable selection ofmaterial in the interjacent lamination or adhesive layer 36, amongothers the advantage will be gained in comparison with the packaginglaminate 20 in FIG. 2 that the quantity or thickness of the layer 35employed as additional gas barrier may be made thinner without thetightness properties of the packaging laminate 30 being negativelyaffected. Examples of such a material in the layer 36 may bepolypropylene (PP) or other olefin polymer with which the thickness ofthe additional gas barrier layer 35 may be made as thin as 5-20 g/m²with gas tightness properties of substantially the same order ofmagnitude as the packaging laminate 20 in FIG. 2 which does not employsuch an interjacent layer of polypropylene or other olefin polymer.

The packaging laminate 30 according to the preferred embodiment of thepresent invention illustrated in FIG. 3 is thus a more economical, butjust as efficient packaging laminate as the packaging laminate 20 for aretortable packaging container which is intended principally forparticularly perishable and oxygen gas-sensitive products such as foods.

It will thus be apparent from the foregoing description that the presentinvention, by merely a simple modification of the prior art packaginglaminate, provides a packaging laminate which, by fold forming andsealing, may be reformed into a retortable packaging containerpossessing sufficiently good tightness properties against gases, inparticular oxygen gas, in order reliably to be able to storeparticularly perishable and oxygen gas-sensitive products such as foods.

Naturally, the present invention is not restricted to the embodimentsillustrated and described by way of example, but numerous variousalterations and modifications are conceivable without departing from theinventive concept as this is defined by the appended claims.

1. A packaging laminate for a retortable packaging container, thepackaging laminate comprising: a core layer having a first surface and asecond surface; a first outer liquid-tight coating on the first surface,the first outer liquid-tight coating being of polypropylene, polyester,high density polyethylene, linear low density polyethylene, mixturesthereof, or a mixture of polypropylene and polyethylene; a second outerliquid-tight coating over the second surface, the second outerliquid-tight coating being of polypropylene, polyester, high densitypolyethylene, linear low density polyethylene, or copolymers of themonomers thereof; an aluminum foil serving as gas barrier and disposedbetween the second surface of the core layer and the second outerliquid-tight coating; at least one additional layer serving as gasbarrier between the second surface of the core layer and the aluminumfoil, wherein the at least one additional layer consists of a materialselected from the group consisting of cyclic olefin copolymers (COC),ethylene vinyl alcohol copolymers (EVOH) and polyvinyl alcohol (PVOH);and at least one interjacent adhesive layer of polypropylene bonding thesecond surface of the core layer to the at least one additional layer.2. The packaging laminate as claimed in claim 1, wherein the core layeris a rigid, but foldable layer of paper or paperboard.
 3. The packaginglaminate as claimed in claim 1, wherein said at least one additionallayer serving as gas barrier consists of an ethylene vinyl alcoholcopolymer (EVOH).
 4. The packaging laminate as claimed in claim 1,wherein the quantity or thickness of said at least one additional layerserving as gas barrier is 10-30 g/m².
 5. The packaging laminate asclaimed in claim 1, wherein the quantity or thickness of said at leastone additional layer serving as gas barrier is 5-10 g/m².
 6. A packagingcontainer comprising a fold formed and thermosealed packaging laminateas claimed in claim 1, wherein the packaging container has been heattreated in a rotort and is gas-tight.
 7. The packaging laminate asclaimed in claim 1, which comprises more than one adhesive layer ofpolypropylene.
 8. The packaging laminate as claimed in claim 1, wherein:the first and second outer, liquid-tight coatings are of polypropylene;and the at least one additional layer serving as gas barrier layerconsists of EVOH.
 9. The packaging laminate as claimed in claim 1,wherein: the first outer liquid-tight coating is of a mixture ofpolypropylene and polyethylene; the second outer liquid-tight coating isof a copolymer of the monomers of (i) polypropylene and high densitypolyethylene or (ii) polypropylene and linear low density polyethylene;and the at least one additional layer serving as gas barrier layerconsists of EVOH.
 10. A packaging laminate for a retortable packagingcontainer, the packaging laminate consisting essentially of: a corelayer having a first surface and a second surface; a first outerliquid-tight coating on the first surface, the first outer liquid-tightcoating being of polypropylene, polyester, high density polyethylene,linear low density polyethylene, mixtures thereof, or a mixture ofpolypropylene and polyethylene; a second outer liquid-tight coating overthe second surface, the second outer liquid-tight coating being ofpolypropylene, polyester, high density polyethylene, linear low densitypolyethylene, or copolymers of the monomers thereof; an aluminum foilbetween the second surface of the core layer and the second outerliquid-tight coating; at least one gas barrier layer between the secondsurface of the core layer and the aluminum foil, wherein the at leastone additional layer consists of a material selected from the groupconsisting of cyclic olefin copolymers (COC), ethylene vinyl alcoholcopolymers (EVOH) and polyvinyl alcohol (PVOH); and at least oneinterjacent adhesive layer of polypropylene bonding the second surfaceof the core layer to the at least one gas barrier layer.
 11. Thepackaging laminate as claimed in claim 10, wherein the at least one gasbarrier layer consists of a material selected from the group consistingof ethylene vinyl alcohol copolymers (EVOH), polyethylene terephthalate(PET), amorphous polyethylene terephthalate (APET), cyclic olefincopolymers (COC), polyamide (PA), amorphous polyamide (APA), liquidcrystalline polymers (LCP) and polyvinyl alcohol (PVOH).
 12. Thepackaging laminate as claimed in claim 10, wherein the quantity orthickness of the at least one gas barrier layer is 10-30 g/m².
 13. Thepackaging laminate as claimed in claim 10, wherein the quantity orthickness of the at least one gas barrier layer is 5-10 g/m².
 14. Apackaging container comprising a fold formed and thermosealed packaginglaminate as claimed in claim 10, wherein the packaging container hasbeen heat treated in a retort and is gas-tight.
 15. The packaginglaminate as claimed in claim 10, which comprises more than one adhesivelayer of polypropylene.
 16. The packaging laminate as claimed in claim10, wherein: the first and second outer, liquid-tight coatings are ofpolypropylene; and the at least one additional layer serving as gasbarrier layer consists of EVOH.
 17. A packaging laminate for aretortable packaging container, the packaging laminate comprising: acore layer having a first surface and a second surface; a first outerliquid-tight coating on the first surface, the first outer liquid-tightcoating being of polypropylene, polyester, high density polyethylene,linear low density polyethylene, mixtures thereof, or a mixture ofpolypropylene and polyethylene; a second outer liquid-tight coating overthe second surface, the second outer liquid-tight coating being ofpolypropylene, polyester, high density polyethylene, linear low densitypolyethylene, or copolymers of the monomers thereof; an aluminum foilbetween the second surface of the core layer and the second outerliquid-tight coating; at least one gas barrier layer between the secondsurface of the core layer and the aluminum foil, the at least one gasbarrier layer consists of a material selected from the group consistingof ethylene vinyl alcohol copolymers (EVOH), cyclic olefin copolymers(COC), and polyvinyl alcohol (PVOH), and the at least one gas barrierlayer has a quantity or thickness of 5-20 g/m²; and at least oneinterjacent adhesive layer of polypropylene bonding the second surfaceof the core layer to the at least one additional layer.
 18. A packagingcontainer comprising a fold formed and thermosealed packaging laminateas claimed in claim 17, wherein the packaging container has been heattreated in a retort and is gas-tight.
 19. The packaging laminate asclaimed in claim 17, which comprises more than one adhesive layer ofpolypropylene.
 20. The packaging laminate as claimed in claim 17,wherein: the outer, liquid-tight coatings are of polypropylene; and theat least one additional layer serving as gas barrier layer consists ofEVOH and has a quantity of 5-10 g/m².